1. Field of Invention
The invention relates to a device for measuring the diffusion and/or absorption and/or refraction of a sample, having a radiation source, at least one receiving element, an optical imaging element and a protection element, wherein the radiation source and the receiving element are arranged on the sensor side of the optical imaging element, wherein the protection element is arranged on the sample side of the imaging element and adjacent to the imaging element, and wherein the radiation source, the imaging element and the receiving element are collectively arranged so that directly transmitted and/or specularly reflected sample radiation can be received by the receiving element.
2. Description of Related Art
Measuring devices of the type mentioned above have been known for quite some time and are used in the fields of chemical analysis and environmental, quality and process control. Such devices are known as encapsulated measuring probes, which are introduced into the control process. In the same manner, such a device can be applied in the context of a large measuring device that, for example, has a sample area for holding the sample to be tested.
A device for detecting diffuse and specular reflection in essentially non-transparent samples is known, for example, from German Patent Application DE 199 20 184 A1 and a device for measuring the diffusion and absorption of samples is known from German Patent Application DE 10 2004 018 754 A1, wherein, here, the major aspect is the examination of essentially transparent samples. At any rate, the devices are similar in that the radiation emitted by the radiation source divergently falls on the imaging element, for example, a lens, and is collimated by the imaging element to a parallel bundle of rays. This parallel radiation strikes the sample, which can be solid, liquid or also gaseous. In the case of transparent sample, the radiation passes through the sample and is reflected by a mirror back to the imaging element, i.e., the radiation passes through the sample twice. In the case of non-transparent samples, the emitted radiation is either specularly reflected or diffusely remitted by the sample and, thus, passes back through the imaging element in the direction of the receiving element.
The radiation source, the imaging element and the receiving element are collectively arranged so that directly transmitted and/or specularly reflected sample radiation can be received by the receiving element. However, the receiving element in the measuring device known from the prior art is not only struck by the transmitted and/or specularly reflected sample radiation, but also by diffusion radiation emanating essentially non-directionally from the sample.
In order to be able to distinguish between the diffusion radiation received by the receiving element and the transmitted and/or specularly reflected sample radiation received by the receiving element, an additional diffusion radiation receiving element is provided, which is collectively arranged in the measuring device so that it essentially can only be struck by diffusion radiation, but cannot be struck by the transmitted and/or specularly reflected sample radiation. Thus, the amount of transmitted and/or specularly reflected sample radiation can be determined from the total radiation determined by the receiving element allowing for the diffusion radiation determined by the diffusion radiation receiving element.
If the transmitted and the specularly reflected sample radiation is to be simultaneously and distinguishably receivable and determinable by the known device, then, not only is one single receiving element necessary, but also an additional receiving element, wherein care should be taken that each of the receiving elements either can only be struck essentially by the transmitted or essentially by the specularly reflected sample radiation, wherein—as is given in the above description—both receiving elements can be struck additionally by diffusion radiation. In the known devices, the radiation source and the receiving element are arranged in a radiation and receiving plane, which runs perpendicular to the optical axis of the imaging element and is essentially located at a distance from the imaging element as is allowed by the focal length. Under this condition, a focused image of the radiation source can be created by the receiving element, or respectively, the receiving elements, which is why radiation running along different optical paths is easily separated from one another in terms of imaging.
However, it has been pointed out that, in practice, in the use of protection elements that are arranged on the sample side of the imaging element and that normally form a transparent separating layer between the sensor part of the device and the sample part of the device, inaccuracies occur while detecting the diffusion and/or absorption and/or refraction of a sample.